Secure electronic memory systems include security devices generally implanted in electronic modules, known as security application modules (SAM). These modules are very important as they contain confidential information, such as bank keys, the discovery of which would enable access to all of the electronic transaction system.
The confidential information to be protected is usually written into an electronic layer of a semiconductor chip, or microchip, with a passivation layer generally covering the electronic layer.
The passivation layer may not be a sufficient obstacle to gaining access to the confidential information, especially if sophisticated means are used to read the information through the passivation layer. Such reading means may utilize scanning techniques of the particle beam type, for example.
Existing security devices for safeguarding the confidential information include devices employing conventional intrusion sensors adapted to protect an enclosure containing the semiconductor chip with the information.
Two other approaches are known which protect the semiconductor chip from exterior reading.
The first approach masks the pattern of the semiconductor chip to be protected, for example by means of metalization, a grid of dummy circuits or a diamond carbon layer.
The second approach stores the confidential information in a volatile RAM type memory and possibly combines it with random numbers that are changed continuously. The information is then accessible only by means of an operating system that controls access. The principles used are identical to those used for cards on which a microprocessor is mounted, also known as smartcards or chipcards. With the second approach, the information contained in the RAM is always lost if the power supply to the semiconductor chip is interrupted. In such case, access to the information is not impossible providing the following are known:
(a) how to remove the covering of the semiconductor chip package when it is active (i.e., ON rather than OFF), without causing short-circuits that would lead to the loss of information, PA1 (b) the exact schematic of the semiconductor chip circuitry, PA1 (c) the memory scrambling table, PA1 (d) the address of the confidential information in the memory, and PA1 (e) the correct manner of writing and reading the address bus and the data bus in real time.
However, the various techniques mentioned hereinabove have the disadvantage of being ineffective if highly sophisticated tampering means are employed or of being costly, particularly when using a diamond carbon layer mask.